The present invention relates to a system for altering the size of an image by a desired magnification and, more particularly, to such a system which electrically alters the effective image size after the image has been scanned and converted into a sequence of electrical sampled scan signals, each of which is representative of the image density at an associated pixel location in a row of pixel locations across the image.
Various optical scanning arrangements are known for scanning the image of a document and converting the scanned image into a sequence of analog or digital scan values representative of the image density at associated pixel areas on the original document. As shown in Monette U.S. Pat. No. 4,216,378, it is known to provide a scanning arrangement in which the light reflected from a document image is projected onto a phototransducer array including a plurality of separate transducers, such as photodiodes or charge coupled devices arranged in a row. A mirror arrangement in the optical system is utilized to sweep the focused document image past the row of transducers, thereby providing for complete coverage of the image.
The transducers may typically be arranged in a row such that they each receive light from a separate small pixel area on the document image. The corresponding pixel areas are arranged generally in a row across the document image. As the scanning of the image takes place in a direction perpendicular to the row of pixel areas, the scan output signals from the transducers are repetitively loaded into an associated shift register and shifted out serially. Thus, the transducer array provides a series of scan signal sequences with the scan values in a sequence corresponding to the image density of respective pixel areas in a corresponding row of pixel areas across the document image. The scan signal sequences may be used to control a printer, such as an ink jet printer, for duplicating or reproducing the original scanned image. Alternatively, the scan signal sequences may be supplied to circuitry providing image enhancement, facsimile transmission, character recognition, or other functions.
It will be appreciated that it may be desirable to be able to alter the effective size of the scanned image. If the scan signals are to be used in a copier or duplicator to control printing, as by an ink jet printer, of the original document image, it is sometimes desired to print either an enlarged or reduced version of the image. If, on the other hand, the sampled scan signals are supplied to a character recognition circuit, it is desirable that the effective size of the character images be enlarged or reduced to a standard character size.
Image reduction or enlargement may be accomplished in several ways. As shown in Miyamoto et al U.S. Pat. No. 4,129,377 and Buddendeck et al U.S. Pat. No. 3,829,209, it is common in xerographic copiers to provide an adjustable lens system which optically alters the size of the image projected onto the photosensitive substrate. Such an optical arrangement is relatively complicated, however, and has numerous disadvantages, including the difficulty in maintaining image edge registration over the entire range of possible enlargements and reductions.
Image reduction or enlargement may also be accomplished electrically in those systems in which electrical scan signals are produced. Borowsky et al U.S. Pat. No. 3,784,981 discloses an electronic image reduction system which is utilized to standardize the height of character images prior to supplying scan signals to a character recognition device. The Borowsky et al system produces eight identical scan signals from each photosensor in a row of photosensors. More than eight of the scan signals are then grouped and averaged to produce adjusted scan output signals. As a result, the adjusted scan output signals are fewer in number than the number of photosensors in the scanning device, thereby effectively reducing electrically the size of the image scanned. In this arrangement, the magnitude of an adjusted scan output signal may be determined by two, three, or four adjacent photosensor outputs, depending upon the degree of image reduction required. The Borowsky et al system is limited in that it is only capable of image reduction and may not be used to enlarge an image.
Similarly, Stoffel U.S. Pat. No. 4,193,092 discloses a magnification system in which the outputs from a row of photosensors are sampled, interpolated, and filtered to produce an analog signal having a voltage which varies in dependence upon the image density of the image across the document. This analog signal is compared with a reference threshold value to produce a binary square wave signal. The binary square wave signal is then sampled at a greater number of points than the number of photosensors to produce "print" or "no print" output signals defining an enlarged image. The Stoffel system is only capable of image magnification and, further, is limited in image resolution since resampling occurs subsequent to production of a binary signal.
Iselen U.S. Pat. No. 3,976,982 discloses an image manipulation system in which reduction of an image is accomplished by taking rectangular cells of pixel scan signals in binary format and applying majority logic to produce a binary "print" or "no print" signal. Enlargement of images is accomplished simply by duplicating scan signals.
White U.S. Pat. No. 4,153,896 and Yamada U.S. Pat. No. 4,163,605 disclose image reduction by simple elimination of stored binary scan data, although averaging between scan data values may also be utilized. Magnification of images is accomplished by duplicating the binary scan data.
Gunning U.S. Pat. No. 4,205,350 discloses a reproduction system in which the scanning speed of an original document is adjusted, while the output printing speed remains constant. As a consequence, when the scanning speed is less than the printing speed, enlargement of the printed image is produced, and when the scanning speed is greater than the printing speed, an image of reduced size is produced.
Wilby U.S. Pat. No. 3,541,245 and Koll et al U.S. Pat. No. 3,272,918 disclose reproduction systems in which digital image data is stored and subsequently supplied to a digital to analog converter. The rate at which the digital image data is read out through the digital to analog converter is adjusted to stretch or to compress the analog output signal, thus providing an output signal representative of either an enlarged or reduced image.
All of the above noted prior art devices have various drawbacks. Some are not capable of providing both image enlargement and image reduction, while others provide for image enlargement simply by redundant usage of scan data signals and image reduction by deletion of scan data signals, thus resulting in a somewhat distorted output of reduced resolution.
Accordingly, it is seen that there is a need for a system for electrically altering the effective size of a scanned image by a selected magnification in which the output scan signals provide a faithful representation of the original image.